1. Related Technical Fields
Related technical fields include route search devices, methods, and computer programs that search for a route from a departure point to a set destination.
2. Related Art
Recently, many vehicles are mounted with a navigation device that enables a driver to easily arrive at his or her desired destination through travel guidance of the vehicle. Note that the navigation device here is a device that can detect a current position of the vehicle through a GPS receiver or the like, acquire map data corresponding to the current position through a storage medium such as a DVD-ROM, a HDD, or the like, or through a network, and display a map on a liquid crystal monitor. Further, the navigation device, which is provided with a route search function that, if the desired destination has been set, searches for the most appropriate route from the departure point (for example, the current position of the vehicle) to the set destination, displays a guidance route on a screen and provides voice guidance if the vehicle has approached an intersection, thereby properly guiding the driver to the desired destination. In addition, recently, some cellular phones, PDAs (Personal Digital Assistant), personal computers, and the like include the same function as the above-mentioned navigation device.
The above-mentioned navigation device and the like take into consideration the congestion of roads when searching for the most appropriate road from the departure point to the destination. Specifically, a route search is performed for example by increasing the search cost for congested roads and decreasing the search cost for uncrowded roads such that the driver can avoid the congested roads and travel along the uncrowded roads by priority.
To acquire congestion information regarding the congestion of roads, the navigation device and the like acquire the congestion information supplied from for example the vehicle information and communication system (VICS®) or acquire the congestion information as center traffic information from a center (for example, a probe center) that distributes center traffic information.
The VICS is a system in which vehicles traveling along roads are detected through sensors installed on roads, an information collecting center (hereinafter, referred to as “VICS center”) collects the detected results and creates traffic information (hereinafter referred to as “VICS information”), and provides a terminal such as a car navigation device, or the like with the information. However, in the above-mentioned VICS, the VICS information can be created only for main roads where the sensors are installed. Therefore, there is a problem that the area of target roads for which the information is provided is limited.
On the other hand, in case of the probe center and the like that distribute the center traffic information, the target area for information collection is not limited like the VICS. Therefore, there is an advantage of being able to collect data from an extremely-large area in real time.
To that end, it has been conventionally proposed to utilize both the congestion information supplied from the VICS and the congestion information acquired from the probe center or the like. For example, Japanese Patent Application; Publication No. JP-A-2003-139556 proposes firstly judging based on the congestion information supplied from the VICS whether a congested section exists on the guidance route, and if it has been judged that a contested section exist on the guidance route, acquiring more detailed traffic information from the probe center.